1. Corticofugal Systems and the Control of Movement Alejandro F. Diaz,MD Maria Antonia Moral-Valencia, MD

2. Motor System Hierarchy

3. Lecture Outline  Corticospinal Tracts – Origin, Course and termination  Corticonuclear Tracts- Origin, Course and Termination  UMN versus LMN signs  Cerebellar and Pallidal influences on Motor output  Pathologic states

4. Corticospinal Systems  Neurons arise from layer V of the cerebral cortex  Betz cells account for only 1-2% of the CST bundle  Found mainly in 6 areas of the brain: Primary motor cortex (MI) Area 4- 31% Premotor cortex Area 6 >60% Supplementary motor cortex Area 6 -29% Post central gyrus Areas 3,1,2 Superior parietal lobule- Areas 5, 7 40% Cingulate gyrus

5. Motor Homonculus  Anterior paracentral area- foot, leg, thigh  Medial 2/3 precentral gyrus-trunk, UE  Lateral 1/3 precentral gyrus-head, face and oral cavity  Disproportion of body part size in the homonculus reflects the density of neurons devoted to the control of a particular region.

6. Corticospinal Tract Course  Motor cortex  Corona radiata  Posterior limb of the Internal Capsule  Middle third of the midbrain crus cerebri  Basilar pons  80-90% cross at the medullospinal junction  Crossed fibers end as the lateral CST ( lateral funiculus)  Uncrossed- anterior CST (ant. Funiculus)

7. Termination of the CST  Topographically organized  Fibers from the frontal lobe synapse in lamina VII-IX of the intermediate zone and ant. Horn  Fibers from the parietal lobe synapse in lamina IV-VI in the posterior horn  Most fibers terminate in the SC enlargements. 55% in the cervical, 25% lumbosacral

8. Corticonuclear System  Consists of cortical neurons that influence the movements of striated muscles of the head innervated by: Cranial nerves V,VII and XII Nucleus ambiguus CN IX and X Accessory nucleus

9. Origins of the Corticonuclear Systems  Originates from the face and head area of the precentral gyrus- face motor cortex  CN III, IV and VI nuclei do not receive input from the face motor cortex. Eye movement is mediated by the frontal and parietal motor eye fields that connect with the midbrain and pontine reticular formation. Not included in the Corticonuclear system.  Corticonuclear fibers send equal numbers of fibers to the left and right motor nuclei in the brainstem with the following exemptions ( predominantly contralateral input): Control of the soft palate and uvula Tongue Lower half of the face

10. Corticonuclear tract Course  Face Motor cortex  Genu of the Internal capsule  At the brainstem they arch superiorly into the: Trigeminal nuclei Facial nuclei Hypoglossal nucleus Nucleus Ambiguus

13. Other Corticofugal Systems  Corticorubral system Cortical projections to the red nucleus from areas 4,6 and to a lesser extent 5 and 7 Primarily influences flexor musculature Supplements the function of the CST.

14. Other Corticofugal Systems  Corticoreticular system Pontine and medullary nuclei give rise to the reticulospinal tracts receive cortical input from the premotor cortex and supplementary motor cortex. Influences extensor muscles including the paravertebral extensors.

15. Other Corticofugal Systems  Corticopontine Axons from nearly all regions of the cerebral cortex contribute to the corticopontine projection. Fontopontine, temporo-, parieto- and occipitopontine fibers synapse with the ipsilateral basilar pontine nuclei which send their axons to the cerebellum. Serves as an important route of communication between th cerebral cortex and the cerebellum

16. Motor Related Cortical Areas  Primary Motor Cortex Functions mainly to EXECUTE movement Does not simply code for flexion and extension of muscles but also the regulation of movement in terms of the amount of force required to make the movement. Motor cortical neurons are informed of the result of their output through the long-latency reflex (sensory info from SI)

17. Supplementary Motor Cortex  Occupies Brodmann Area 6  Contain a less precise homonculus  Receives input from the parietal lobe  Projects to the MI and reticular formation of the Spinal Cord  In contrast to single muscle movements of the MI, these involve sequences or groups of muscles and orient the body or limbs in space.  ORGANIZING and PLANNING of movement

18. Premotor Cortex  Occupies a portion of Area 6  Contains a less precise somatotopic representation of the body musculature  Receives input from the sensory areas of the parietal cortex  Projects to the MI and reticular formation of the Spinal cord  Involved in PREPARATION to move  Organizes the postural movements required to make a movement.

19. Posterior Parietal Cortex  Comprised of Brodmann Areas 5 and 7  Carry out “background computations” for movements in space.  Project to the supplementary motor and premotor cortices with few spinal and brainstem targets  Area 5 receives projections from the somatosensory areas and vestibular system (hand manipulation neurons)  Area 7 processes visual information related to the location of objects in space (eye-hand coordination neurons)

20. Cingulate Motor Cortex  Because of the proximity to the limbic lobe, these may be involved in movements that have an intense motivational or emotional component

22. Final Common Pathway

23. UMN versus LMN Signs  LMN SIGNS Flaccid paralysis Atrophy Fibrillations and fasciculations Hypotonia Areflexia  UMN SIGNS Initially flaccid paralysis which becomes spastic Hypertonia Hyperreflexia Pathologic reflexes e.x. Babinski sign

25. Cerebellar and Pallidal Influences  Cerebellar nuclei and Globus Pallidus project to the ventral anterior and ventral lateral and oral parts of the ventral posterolateral nuclei of the dorsal thalamus.(motor areas of thalamus)  Motor areas of the thalamus gives rise to thalamocortical projections. Pallidal origins project mainly to the supplementary motor cortex and cerebellar inputs project to the Primary motor cortex.

26.  Signal transmission in the CST and CNT systems can be modified by outputs from the cerebellum,basal nuclei and thalamus

31. DIRECT PATHWAY NET EFFECT: ↑ activity of the thalamus  excitation of the cerebral cortex

33. INDIRECT PATHWAY NET EFFECT: ↓ activity of thalamus  ↓ activity of the cerebral cortex

37. What happens in Parkinson’s Disease?

41. Motor Loop

44. Hypokinetic Disturbances  Akinesia- impairment in the initiation of movement secondary to an impairment in the ability to plan or guide a movement  Bradykinesia- a reduction in the velocity of and amplitude of movement due to the imbalance of outflows to the thalamus of the direct and indirect pathways.  Both are characteristic of patients with Parkinson’s disease  Considered as lesions of the neostriatum causing the thalamus to not be disinhibited leading to a decrease flow of information through the thalamus to the cortex

45. Hyperkinetic Disturbances  Take the form of dyskinesias  Ballismus- uncontrolled flinging (ballistic) of an extremity, most commonly seen in lesions of the contralateral subthalamic nucleus  Chorea- generalized irregular ( brisk) dance-like movements of the limbs  Athetosis- continuous writhing of the distal portions of the extremity  Caused by the disruption of the indirect pathway resulting in the loss of excitatory subthalamopallidal neurons

46. Cerebellar influences  Vestibulocerebellar module- (archicerebellum) influences posture, balance and equilibrium including orienting the eyes during movement. Deficits produce: ataxia, titubation, nystagmus and deficits in pursuit eye movements

47. Cerebellar influences  Spinocerebellar module- focused primarily on the control of axial musculature through the vermis and fastigial efferents and the limb throught the globose and emboliform nuclei.

48. Cerebellar influences  Pontocerebellar module- functions in the planning and control of precise dexterous movements of the hand, arm, forearm and in the timing of these movements.  Lesions in the cerebellar hemisphares result in motor deficits on the ipsilateral side of the body.

49. Disturbances  Decomposition of movement- dyssynergia  Hypotonia  Ataxia  Dysmetria (past-pointing)  Kinetic or intention tremor  Dysdiadochokinesia awkward rapid alternating movements  Rebound phenomenon or impaired check  Dysarthria  Nystagmus

51. Summary  Motor system control is achieved by parallel systems formed by somatotopically organized, descending cortical projections that link the various motor related areas of the cortex more with spinal motor circuits.  Such that each pathway contributes its own element or series of elements to movement control.